What is 'Negative Energy' in science?
Negative Energy, the end of the universe, and time travel.
“Some say the world will end in fire, some say in ice…” says Robert Frost
The energy in a system is constant. It can be transformed from one form to the other but cannot be created or destroyed. Many of the theories and explanations on how our universe (physics) works are based on this law of conservation of energy.
We need to understand the future of the universe to understand the concept of Negative Energy. Negative energy is basically used to understand the nature of certain fields like the gravitation field.
How is the universe going to end?
There are two theories that explain how the universe is going to end. Two hypothetical theories suggested are the Big Rip or the Big Crunch.
The Nobel Prize awarded for physics in 2011 was divided among a group of two between three individuals. Brian P. Schmidt and Adam G. Riess were one group of scientists who received the award for the discovery of the accelerating expansion of the universe. They observed a supernova come to the conclusion. They theorise that the universe is expanding at a faster rate and if it continues to expand it will end up in ice.
The Big Crunch suggests that the universe will ultimately stop expanding at some point in time, mainly because of the dense matter present in it. The gravity present will also cause a reversal in the direction of the universe and ultimately collapse. A new Big Bang will start after the collapse.
Looking at the current observations, the chances of the Big Rip are more probable as compared to the Big Crunch.
The Negative energy:
If the universe starts collapsing, two bodies will attract each other with the gravitational field as they come closer. So, both the kinetic energy and gravitational energy is going to increase in the process. This contradicts the law of conservation of energy.
Theories suggest that a universe with negative energy will keep on expanding. If the bodies are very far from each other, the gravitational energy is close to zero.
Negative Energy, Wormholes and Time Travel:
Wormholes are speculative structures suggested by the Einstein Field Equations. The equation explains the spacetime geometry. It suggests that time travel as the two ends of a Wormhole is located in different spacetimes. The existence of Wormholes is also based on the presence of negative energy.
Theories suggest that a Wormhole that can operate in both the directions needs exotic matter with negative energy density to stabilise it. Exotic matters are materials that have negative mass/energy.
Many other hypothetical theories related to time travel like faster than light travel and warp drive require the presence of negative energy.